One of the hardest parts of eating healthily, or following a diet, is the cravings. Whether your taste be for cronuts, cheeseburgers or gooey chocolate brownies, cravings often have the power to sway us towards less healthy food choices at times when we're trying to only put the right things in.
But there’s growing evidence to suggest that sugar itches aren’t simply a matter of 3.30-itis, but rather a result of the community of bacteria that live in your gut.
Humans are crawling with bacteria. A recently study led by the Weizmann Institute of Science cites that we have roughly as many bacteria cells in our bodies as human ones, equating to between 30 and 50 trillion in total.
The more you feed them, the more they grow
A large community of these bacteria live in our gastrointestinal tract and are collectively known as the gut microbiota. A diverse population of different types of gut bacteria has been linked to good health, but as Dr Paul Bertrand, the head of RMIT University's gut neuroscience laboratory explains, it’s a dog eat dog world down there.
“In your lower gut, the bacteria are constantly fighting with one another for real estate to establish themselves,” Dr Bertrand tells SBS.
The more a certain type of bacteria is fed, the larger its colony grows - and that all comes down to what we put in our mouths.
“The bacteria are not like people, they’re not generalists. A lot of the bacteria can only survive on certain kinds of things, they have pretty strict preferences in some cases," Dr Bertrand explains.
“Some of them might be able to digest sugars better than fibres or anything else, so if you eat those kinds of sugars, then they win and get lots of food and more space in your gut to grow into a bigger colony.”
The bigger the colony, the more influence that type of bacteria gains in your gut, which is when it can start to cause havoc with unhealthy cravings.
“If you have a high sugar diet and if there’s a really large population of sugar-loving bacteria down there that have sort of taken over and you deprive them suddenly of their sugar, they get angry and they can produce bacterial toxins which may well make you feel poorly”.
These mood-altering toxins induce an unhappy or uneasy feeling that tempts us to reach for the foods the bacterial colonies like - which in this case would be sugary ones.
Their health above yours
In a 2014 paper, researchers from UC San Francisco, Arizona State University and University of New Mexico explain that “microbes in the gastrointestinal tract are under selective pressure to manipulate host eating behaviour to increase their fitness, sometimes at the expense of host fitness".
“Microbes may do this through two potential strategies: generating cravings for foods that they specialise on or foods that suppress their competitors, or inducing dysphoria (feeling down and uneasy) until we eat foods that enhance their fitness.”
The researchers go on to hypothosise that a “lower diversity in gut microbiome should be associated with more unhealthy eating behaviour and greater obesity”.
While much is still to be learnt about human gut bacteria, evidence from tests on mice show that their gut bacteria can have an influence over sugar preferences and brain chemistry and can even alter taste receptors to affect eating behaviour in a way that is favourable to their food preferences - regardless of whether those preferences are good for the host's health.
Many animal tests however, have been comparing mice who have gut bacteria and those that don’t have any bacteria at all - something which isn’t the case in humans.
Communication is key
The gut and the brain are very much in tune and there are a number of potential ways our bacteria use this relationship to exert influence over cravings as well as to communicate other more basic sensations such as feeling hungry or full.
As Dr Bertrand explains, “the gut has its own little brain and its own nerves and it sends projections out to the rest of the body. The central nervous system - the brain - via the vagus nerve, has its own sensors in the gut so there’s a bi-directional communication between the brain and the gut neurons and that’s where a lot of the control happens.
“The gut bacteria probably influence that relationship as well as release toxins into the blood that influence the normal relationship between the gut and the brain.”
When it comes to making you feel full, “a happily functioning gut releases hormones which tell the body that there are nutrients around and everything is fine, and some of these hormones might get into the brain and act on the brain centre which controls feeding and makes you feel satisfied.”
How to lessen their grasp
Dr Bertrand says that lessening the bacteria’s influence on your cravings for sugary and fatty treats is all about “changing the makeup of your bacteria more gently so you don’t stress them out too much”.
“It’s really easy to change the bacterial makeup of your gut, anything you put in your mouth is going to change the bacterial composition unless it’s all processed sugar,” he says. “If you’re eating any kind of whole food that has stuff in it that you can’t digest that’s feeding the bacteria."
"Normally your gut is really good at getting all of the nutrients out of the food, so it extracts most of the nutrients and they don't actually get down to the large intestine which is where all of the bacteria live - so what the bacteria mainly live on is what you can’t digest.
“There’s a lot of different bacteria and they like lots of different foods but fibres and resistant starches are the ones that people think are probably the better ones. So if you eat lots of these, you’re feeding bacteria that can digest some of that fibre or digest the resistant starches and those bacteria are generally meant to be healthier bacteria."
He explains that "from a scientific point of view, it’s very clear that the more varied your diet is, the more varied the microbacteria that you support, so if you eat lots of different kinds of foods with different sorts of undigestable products, that supports a more diverse microbacterial community in your gut and that’s been associated with good health and a more robust ability to resist stress and change.”